Digital Repository, Giornata IGF Forni di Sopra (UD) 2011

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Non-proportional mixed mode plasticity, crack tip fields from digital image correlation
S. Pommier, P.Y. Decreuse

Last modified: 2011-02-25


This paper is devoted to the experimental analysis of I+II mixed mode plasticity at crack tip using
digital images correlation. The method employed to post-treat the experimental velocity fields is the same as
that used in previous papers to post-treat finite element computations. The experimental velocity field is first
partitioned into mode I and mode II components using symmetry considerations with respect to a coordinate
system attached to the crack tip. Each mode is then partitioned into elastic and plastic parts. Each part is finally
expressed as the product of an intensity factor and of a shape function, constructed once for all for a given
material. With this approach, the experimental crack tip velocity field is fully characterized by four degrees of
freedom, which are respectively the intensity factors of the elastic and plastic part for each
mode. The experimental results showed that the error associated with this approximation remains small. The
error is also used for the determination of the yield surface of the crack tip region. The results show that the
elastic domain of the crack tip region can be displaced in a KI ,KII space according to the plastic history
experienced by the crack tip region. In addition, complex and non-intuitive evolutions of mixed mode plasticity
were measured and explained with respect to the plastic history.

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